The present invention relates to a device for controlling a gearshift of a transmission, and more particularly, a gearshift control device for a transmission of the type which includes a gearshift having first and second pressure medium chambers which are separated from each other by a piston that can be moved in the direction of its longitudinal axis, first and second controllable valve systems via which the first and second pressure medium chambers can be respectively connected selectively to a pressure medium source or sink, and an electrical control system to actuate the valve systems.
A device of this type is disclosed, for example, in DE 33 15 221 C2. Such known device includes a first controllable valve system and a second controllable valve system, by means of which a first pressure medium chamber and a second pressure medium chamber of a gearshift can be selectively connected to a pressure medium source or to a pressure medium sink. The gearshift is provided with a piston and a piston rod, whereby the piston can be moved by the pressure medium in the pressure medium chambers in the direction of its longitudinal axis. The piston rod is connected via a lever to the selection shaft of a transmission. In addition, the device is provided with a pressure-medium actuated retaining device for the selection shaft of the transmission. The retainer device can be selectively connected to the pressure medium source or to the pressure medium sink by means of a controllable valve system. The controllable valve systems are connected to an electrical control system.
To shift the transmission, the retainer device is first brought into its disengaged position by subjecting it to the pressure medium. The piston of the gearshift, which is connected to the selection shaft, is then driven by introducing pressure medium into the first pressure medium chamber of the gearshift. Shortly before the selection shaft has reached the desired position, the retaining device is vented. The force of a spring of the retaining device causes part of the retaining device to go into a position in which the retaining device brakes the selection shaft. At the same time, the feeding of the pressure medium to the pressure medium chamber of the gearshift is stopped. When the selection shaft has reached the desired position, it is retained in this position by the retaining device. The shifting of the retaining device from the disengaged position to the braking or holding position, and the termination of the pressure medium feeding to the pressure medium chamber of the gearshift, take place as a function of the position or as a function of the running speed of the selection shaft of the transmission.
Among other things, the controlled retaining device in accordance with the known gearshift control device prevents the piston to move beyond the desired position in the course of a positioning process (overshooting of the piston). This overshooting of the piston is caused, in part, by the fact that the pressure in the pressure medium chamber of the gearshift rises relatively abruptly in the course of a positioning process, in order to be able to exert a force on the piston and thereby on the selection shaft sufficient to disengage the selection shaft from a fixed position. The steep rise in pressure in turn causes the piston to move at relatively high speed in the direction of its predetermined holding position.
It is the object of the invention to provide a device for the control of a gearshift of a transmission that can be fabricated simply and effectively.
In accordance with these and other objects of the invention, there is provided a gearshift control device for a transmission which includes a gearshift having a first pressure medium chamber and a second pressure medium chamber which are separated from each other by a piston movable in a direction of its longitudinal axis. A first controllable valve system is provided, via which the first pressure medium chamber is selectively connectable to a pressure medium source or to a pressure medium sink. The first controllable valve system includes a pressure medium input, a first pressure medium outlet connected to the first pressure medium chamber and a second pressure medium outlet. A second controllable valve system is also provided, via which the second pressure medium chamber is selectively connectable to the pressure medium source or to the pressure medium sink. The second controllable valve system includes a pressure medium input, a first pressure medium outlet connected to the second pressure medium chamber, and a second pressure medium outlet. The gearshift control device further includes an electrical control system for actuating the first and second controllable valve systems. A third controllable valve system is also provided, and which is controllable by operation of the electrical control system. The third valve system is connected to the first controllable valve system and to the second controllable valve system, as well as to the pressure medium source, in such manner that the pressure medium input of the first controllable valve system and the pressure medium input of the second controllable valve system can be selectively connected to the pressure medium source or can be closed off against said pressure medium source. The gearshift control device further includes a pressure sensing device for measuring a first pressure in the first pressure medium chamber and a second pressure in the second pressure medium chamber, the pressure sensing device being connected electrically to the electrical control system. The electrical control system is designed and linked to the pressure sensing device and the controllable valve systems in such manner that actuation of at least one of the controllable valve systems can be rendered dependent upon at least the signals of the pressure sensing device.
The invention provides the particular advantage that the actuating force of the gearshift can be controlled by simple means in a pressure-dependent manner. The device according to the invention is simple in structure and economical in its manufacture.
In a particularly advantageous further development of the device according to the invention, the pressure medium connection of a pressure sensing device, consisting of only one pressure sensor, is connected to a pressure medium pipe which connects the first controllable valve system and the pressure medium input of a second controllable valve system of the gearshift to the pressure medium outlet of a third controllable valve system, a pressure medium input of which is connected to a pressure medium source. Such configuration makes it is possible to measure the degree of pressure in either of the two pressure medium chambers using only one pressure sensor, as well as to monitor the level of the supply pressure for the gearshift.
In another advantageous further development of the invention, the pressure medium inputs of two additional valve systems assigned to the two pressure medium chambers of a second gearshift are connected to pressure medium pipes connecting the pressure medium outlet of the third valve system to the pressure medium inputs of the two valve systems of the first gearshift and of the pressure sensing device. By virtue of this further development of the invention, two gearshifts with only one additional valve system and only one pressure sensing device can be very easily controlled through pressure. The pressure in each pressure medium chamber of the two gearshifts and the supply pressure can be measured with only one pressure sensing device.
A choke is advantageously installed between the pressure medium outlet of the third controllable valve system and the pressure medium inputs of the two controllable valve systems of the gearshift. The choke prevents the pressure on the pressure sensing device to rise to the level of the supply pressure during the control phase. The pressure at the pressure sensing device is therefore closer to the pressure in a pressure medium chamber of the gearshift.
The gearshift is advantageously equipped with a distance sensor, so that the piston of the gearshift can be brought into any predetermined position as a function of the signals of the distance sensor.